JANSI-FDE-03 rev.1

Assessment Methods for Nuclear Power
Plant against Fault Displacement(Provisional Translation of Main Text)

September 2013
On-site Fault Assessment Method Review Committee
Japan Nuclear Safety InstituteRevision History
Date

VersionSummary

Sep. 2013

JANSI-FDE-03

Apr. 2014

JANSI-FDE-03 rev.1

Note

Correction of errors

Disclaimer
This report was enacted after discussions by committee members and participants with expert
knowledge and interest at the “On-site Fault Assessment Method Review Committee” which wasestablished by the Japan Nuclear Safety Institute (JANSI).
JANSI is accountable for the content of the report, but is not responsible for any problems that
may arise through use of the report. In addition, JANSI does not approve or guarantee inspections,assessments, and other actions that are conducted in accordance with the report.
This is tentative translation of main text of the “Report on Study and Analysis of Fault
Displacement Assessment Methods for Nuclear Power Plant Sites” JANSI-FDE-01 © Japan
Nuclear Safety Institute, (2013). The authentic version of this material is the Japanese language
version. JANSI makes no warranty and assumes no responsibility for the accuracy or quality.
COPYRIGHT NOTICE: Permission to reproduce or translate the information contained inthis document may be obtained by writing to JANSI, 5-36-7 Shiba, Minato-ku, Tokyo 108-0014,
JAPAN

Contents
1. Introduction......................................................................................................................... 1
2. Definition............................................................................................................................ 2
3. Scope of Application ............................................................................................................ 4
4. On-site Fault Assessment Policy ........................................................................................... 5
5. Fault Survey Method and Classification .............................................................................. 11
6. Methodology of Estimation of Fault Displacement ............................................................... 13
7. Load Combinations and Allowable Limits ........................................................................... 28
8. Safety Assessment of Buildings and Structures against Fault Displacement ............................ 30
9. Safety Assessment of Components and Piping Systems against Fault Displacement ................ 37
10. Summary ........................................................................................................................... 46
Reference;
The Committee Members, Presenters, and Secretariat, Date of Meeting
Appendices (in Japanese)
A. Fault-Related Terminology
B. Findings from Secondary Fault Survey
C. Probabilistic Fault Displacement Hazards
C-1 Examples of Fault Displacement Hazard Computation
C-2 Application of Probabilistic Fault Displacement Hazard Analysis Method in Japan
C-3 Findings from Review of Diablo Canyon Power Plant
D. Behaviors of Buildings and Structures due to Fault Displacement
D-1 Fracture Properties of Reinforced Concrete Members
D-2 Trial Analysis of Buildings and Structures Affected by Fault Displacement (BWR Buildings)
D-3 Trial Analysis of Buildings and Structures Affected by Fault Displacement (PWR Buildings)
E. Safety Assessment of Components and Piping Systems against Fault Displacement
E-1 Summary of Impact on Equipment from Inclined or Deformed Buildings and Structures
E-2 Examples of Trial Analysis of Impact on Connecting Pipes from Relative Displacement
between Buildings
F. Overseas Standards and Guidelines Concerning On-site Faults

1.

Introduction
One of the major regrets about the accident that occurred at Fukushima Daiichi Nuclear Power
Station on March 11, 2011 was that we were not able to consolidate our knowledge due to weak
coordination across the areas concerned with tsunami measures, such as “seismic analysis”,“tsunami analysis”, “civil engineering design”, “component design” and “safety design”. With
deep reflection on this point, it is extremely important to consider comprehensive measures bycoordinating relevant areas, consolidating our knowledge, and grasping a complete picture invarious activities to improve nuclear safety in the future.
For on-site fault assessment, it is really necessary to put together scientific and engineering
wisdom and review the safety of facilities in a comprehensive manner. In Japan as an earthquake
country, a great deal of studies and researches into earthquakes have been accumulated in theareas of both science and engineering over the years. The world’s leading highest level ofknowledge has been accumulated. To improve nuclear safety, it is considered vital to draw on all
intellectual resources for full utilization.
From the above perspective, this report shows the procedure to comprehensive assessment ofplant safety against fault displacement, drawing on all knowledge in the areas of“geomorphology”, “geology”, “geophysics”, “seismology”, “geotechnology”, “earthquake
engineering”, “structural engineering”, “nuclear safety engineering”, and so forth. In other words,
this report does not focus just on whether an on-site fault may be an active fault. Rather, it isintended to show a scientific and engineering framework to examine “whether it has a significant
impact on the safety functions of important nuclear power plant facilities” when there is grounddeformation due to fault movement in the ground on which they are sited.
This report summarizes the procedure from the estimation of fault displacement to theassessment of plant safety against displacement, which has not conventionally been made clear. It
does not contain detailed analyses or specific study examples. These details will be deliberated
further in the future.
We hope that this report will contribute to the improvement of nuclear safety.

12. Definition
As described in 1. Introduction, this study shows the procedure to comprehensive analysis of plantsafety against fault displacement, drawing on all knowledge in the areas of “geomorphology”,“geology”, “geophysics”, “seismology”, “geotechnology”, “earthquake engineering”, “structural
engineering”, “nuclear safety engineering”, and so forth.
For a cross-cutting study like this, it is important to clarify the definitions of the terms and sharethem with the parties concerned. For this purpose, the terms with different definitions from one area
to another have been sorted out to establish a framework for a coordinated study. Thus, some of theterms used in one area may not always be used in the same way in other areas.
Table 2-1 shows the definitions of the terms used in this report.
Fault-related terms and their definitions have been put together and sorted out in Appendix A.

Term
Fault
Active fault

Earthquake source
fault
Surface earthquake
fault
Master fault
Splay fault

Secondary fault

LandslideOn-site fault
Ground deformation

Geological field

Fault gouge
Ground deformation
analysis
Enforceddisplacement analysis
Foundation groundstability analysis

Table 2-1: Definitions of Terminology
Definition
A discontinuous plane created by the fracture of rocks, along which
relative displacement has occurred
In general, a fault that has repeatedly been active in recent geological ages
and may possibly be active in the future. A fault that cannot be denied
being active since the Late Pleistocene.
In recognizing active faults, a fault, which made no displacement or
deformation in geological layers or geomorphic surfaces of the lastinterglacial period or before, can be set outside the scope of consideration.
A fault that is considered to have caused an earthquake
A fault that has come up to the ground surface
Same as an earthquake source fault
A fault that is formed diverging from an earthquake source fault and has apotential to be active in the future due to the activity of the earthquake
source fault
A fault that is formed secondarily in association with the activity of anearthquake source fault although no geotectonic association with theearthquake source fault and the possibility of its displacement cannot bedenied in the future by the activity of the earthquake source fault
Phenomenon in which materials of a slope slide by gravity
A fault, the outcrop of which exists on the site of a nuclear power plant, orthe existence of which has been confirmed by boring survey, etc.
Displacement bordering with a fault plane (hereafter referred to as
displacement or fault displacement) and continuous deformation, such as
inclination (hereafter referred to as deformation)
Geological environment at the relevant site in the past and present, e.g.,
formation environment, geological structure formation process, and stressfield.
Fine-grained materials formed by fault movement
Analysis to examine the deformation (displacement and/or deformation)of the foundation ground of a reactor building, etc.
Analysis in which the displacement is input as a displacement vector at
the boundary of the model
Analysis to verify that the support function of the foundation ground of areactor building , etc. is not significantly affected by seismic motion or
ground deformation, including the examination of a slip safety factor aswell as the stress state of the ground2

An earthquake occurs upon displacement or fracture of an earthquake source fault. When the scaleof displacement is major, it will come up to the ground surface as a surface earthquake fault. Active
faults are the traces of activities of earthquake source faults that had repeatedly appeared at the
ground surface, which include “master faults” and “splay faults”.
A “secondary fault” is a fault that is formed secondarily in association with the activity of anearthquake source fault although no geotectonic association with the earthquake source fault and thepossibility of its movement cannot be denied in the future by the activity of the earthquake source
fault
Surface earthquake fault

Earthquake source fault= master fault
Seismogenic layer

Figure 2-1: Schematic Diagram of Relationship between Earthquake Source Fault and Surface
Earthquake Fault
Secondary fault
Secondary fault
Secondary fault

Secondary fault

Splay fault
Master fault

Quaternary

Basement rock

Basement rock

Figure 2-2: Conceptual Diagram of Surface Earthquake Fault Distribution3

3.

Scope of Application(i) This study shows the framework of the safety assessment of a nuclear power plant against
on-site fault displacement. When considering the impact of on-site faults in the event of anearthquake, seismic motion (quake) and ground deformation (discontinuous displacement andcontinuous deformation) come into question. This report focuses on the latter, i.e., grounddeformation.
(ii) An on-site fault is a fault, the outcrop of which exists on the site of a nuclear power plant, orthe existence of which has been confirmed by boring survey, etc. When the displacement of thisfault cannot be denied in the future, it has the potential to affect the facilities. In this study, both
displacement and deformation will be considered as a direct or indirect effect on the facilities.
The safety assessment of a nuclear power plant against on-site fault displacement, which takes
account of both impacts, will be referred to as “safety assessment against fault displacement”.
・Direct impact: Impact due to discontinuous displacement of the ground (hereafter referred
to as “displacement”)
・Indirect impact: Impact due to continuous deformation, such as inclination (hereafterreferred to as “deformation”)(iii) In this study, those faults whose possibility of movement cannot be denied in the future will
be considered. In other words, those faults that have possibility of passively moved by seismic
activities (secondary faults) will be considered in addition to active faults (master faults andsplay faults) that are regarded as earthquake sources. After considering the possibility of thefault movement in question, the impact of its displacement on the facilities will be analyzed
when the possibility of displacement cannot be denied. On the other hand, those faults that canbe denied to have been active since the Late Pleistocene are regarded not to move in the future.
(iv) On-site faults confirmed at the outcrop on the bed rock surface are considered. When there isno evidence on the bed rock surface, the occurrence of new faults does not have to beconsidered.
(v) This study focuses on the important facilities mainly among power reactor facilities concernedwith “shutting down”, “cooling” and “containing”. For example, these include reactor buildings
and components and piping systems in them. This study is also considered applicable toimportant civil engineering structures, and other nuclear-related facilities.
(vi) The analysis methods shown in this report have been developed primarily for application toexisting plants. These methods can also be referenced in the design of new plants.

44. On-site Fault Assessment Policy
The basic idea is to ensure that “the safety functions of the reactor facilities would not
significantly be affected” by earthquakes and/or tsunamis, as well as other natural phenomena
than earthquakes and tsunamis. Safety against displacement will also be assessed taking accountof its effect on these safety functions.
4.1 Safety Assessment of Plant against Fault Displacement
The flowchart of safety assessment against fault displacement is shown in Figure 4-1.
(i) Grasp the distribution, properties, and activity of on-site faults through geological surveys.
Select the secondary faults whose movement cannot be denied in the future.
(ii) Estimate the displacement of the selected secondary faults by the method described in Section
4.2 to set the design basis displacement δa that is equivalent to the design basis event forother natural phenomena. In doing so, the probabilistic fault displacement hazard analysis, inwhich the fault in question is regarded as a secondary fault, will be referenced. Here,referencing means to estimate the annual frequency of exceedance of δa based on theprobabilistic fault displacement hazard analysis so as to verify that the estimated value meetsthe reference value shown in the next section. Use the method described in Chapter 6 toperform a stability evaluation of foundation ground in the event of fault displacement so as toverify that the foundation ground will retain the function to support the buildings andstructures.
(iii) In estimating the design basis displacement δa, perform an enforced displacement analysis
by the method described in Chapter 8 with the obtained ground displacement as a condition
input to the analysis model of the buildings and structures. Separately, determine the impactof seismic motion on the buildings and structures to grasp the effect of both displacement andseismic motion on the buildings and structures, thereby confirming that the safety functions
will not significantly be affected in comparison with the allowable limits described in Chapter
7. The deformation and inclination of building mat slabs, etc., and the relative displacement
between the buildings will be used as input conditions for reviewing components and piping
systems.
(iv) Use the deformation, inclination, and relative displacement between the buildings obtained in
the foregoing examination of the buildings and structures to estimate the effect oncomponents and piping systems. Use the method described in Chapter 9 to analyze safety
against displacement. When it is anticipated that the safety functions may be affected, safety
improvement measures need to be taken.
(v) Since the uncertainty of fault displacement is considered to be greater than that of othernatural phenomena, the impact on the facilities arising from the displacement exceeding thedesign basis displacement δa will be examined from the perspective of risk assessment. That
displacement will be referred to as the beyond design basis displacement δb. In this case, ananalysis will be performed based on the actual strength of each piece of equipment toestimate its impact on the functions required of the facilities. When the functions required of
the facilities are considered to be affected, mitigation measures will also be considered.
Probabilistic fault displacement hazard analysis in this stage is intended to refer the annual
frequency of exceedance of δb from the perspective of risk assessment.

5

Detailed geological survey

Grasp the distribution, properties, and activity of faults

Yes

Activity since the Late
Pleistocene can be denied

Do not consider displacement

No
Select faults to consider displacement

Probabilistic Fault
Displacement Hazard
Analysis (PFDHA)

Estimate fault displacement
a. Estimate by geological survey results
b. Estimate by analysisc. Sort out surface earthquake fault data

Set the design basis displacement δaReferencing
Safety improvement measures

Analysis for buildings and structures against fault displacement

Evaluate the effect on components and piping systems

Maintain safety functions for the design basis
displacement δaNo

Yes
Referencing
Review with the beyond design basis displacement δbEndApply mitigation measures

Figure 4-1: Flowchart of Assessment

64.2 Estimating Fault Displacement
4.2.1 Basic Approach(i) It is reasonable to treat fault displacement in an approach consistent with earthquakes,
tsunamis, and other natural phenomena that are taken into account in deliberating how toensure nuclear power plant safety. It should be verified that the maintenance of safetyfunctions would not significantly be affected even if fault displacement should occur in the
ground in the event of an earthquake.
(ii) The activity and origin of an on-site fault need to be studied in a scientific and reasonable
manner. When different opinions arise as to its activity and origin, however, it is important
to show that its effect on the facilities can be estimated through an engineering analysis
even when the fault displacement occurs.
(iii) For a nuclear power plant, since the location of installations is decided based on a detailed
study, no active fault exists beneath the reactor building. In this report, the secondary fault
that exists immediately beneath the reactor building and the possibility of its displacement
cannot be denied is considered, and its displacement will directly be applied to the reactor
building. The effects of other on-site secondary faults and master faults that exist both on
and off the site on the ground on which the reactor facilities are sited will also be analyzed(iv) Core damage frequency (CDF) of 10-4 (per year) has been specified as a performance goal
to ensure nuclear power plant safety. Based on this, the probability (frequency) of natural
phenomena has been discussed.
(v) With regard to seismic motion, it is required to perform a seismic hazard analysis to showwhat level of exceedance probability is comparable to the Design Basis Earthquake Ground
Motion Ss. The probability (frequency) of Ss is set to be 5×10-4 to 10-5 (Nuclear Power
Plant Seismic Design Engineering Codes JEAC4601-2008). In the examination guideregarding tornadoes, the annual probability of exceedance of the maximum wind velocity ofthe design basis tornado is considered to be 10-5 (tentative) as new regulatory standard.
Based on these, in this report, annual frequency of exceedance of 10-4 to 10-5 (per year) is
assumed for design basis fault displacement. This fault displacement will be referred to as
the design basis displacement δa.
(vi) For this design basis displacement δa, it is necessary to ensure the safety functions of a
nuclear power plant, i.e., “shutting down”, “cooling” and “containing”.
(vii) Since the uncertainty of fault displacement is considered to be larger than that of othernatural phenomena, the impact on the facilities arising from fault displacement exceeding
the design basis displacement δa (beyond design basis displacement δb) will be examined.
4.2.2 Estimating Displacements (δa and δb) for Analysis
It is usual that a large number of faults exist both on and off the site. Out of these, the faults
for which the effect of displacement will be estimated are classified as shown below. Faults
whose activity since the Late Pleistocene is denied are considered not to move in the future.
(i) Secondary fault immediately beneath the reactor building
Estimate the displacement of the secondary fault in question in the event of an earthquake
and apply this displacement to the facilities.
(ii) Secondary faults not immediately beneath the reactor building
Estimate the displacement of the secondary fault in question in the event of an earthquake toanalyze the effect of this displacement on the facilities (ground deformation, such as theinclination of the ground).
(iii) Master faults and splay faults that exist on and off the site
Estimate the displacement of the master fault in question in the event of an earthquake toevaluate the effect of this displacement on the facilities (ground deformation, such as theinclination of the foundation ground). Also examine whether the on-site secondary faults
will be displaced by the displacement of the master fault. When they are displaced, (i) or (ii)7should be considered.
(1) Design basis displacement δa
The design basis displacement δa will be estimated in a comprehensive manner by any ofthe methods (a, b, c) listed below or by appropriately combining them.
a. Estimation by geological survey results
When past fault activity data is available from on-site geological surveys, δa will be
estimated based on it. Specifically, it can be estimated as displacement or deformation
per activity from trench surveys, etc., or can be computed from the cumulative
displacement and the number of activities.
b. Estimation by analysis
If no geological survey results are available as shown in a above, δa can be estimatedusing the analysis method described below. In this case, the per-activity displacement ofmaster faults that exist on and off the site will be estimated and the δa of the secondary
fault immediately beneath the facilities will be estimated based on it by analysis. The
per-activity displacement of a master fault can appropriately be estimated based on thegeological survey results or the empirical relationship between the master fault
displacement and the magnitude of earthquake.
c. Probabilistic fault displacement hazard analysis
Based on the above mentioned estimations (a. and b.), an appropriate δa is set basedon engineering judgment. The annual frequency of exceedance of this δa will be
estimated based on the probabilistic fault displacement hazard analysis to compare withthe reference value of 10-4 to 10-5 (per year).
(2) Beyond design basis displacement δb
In view of the uncertainties involved in natural phenomena, the impact on the facilities
arising from any displacement (beyond design basis displacement δb) exceeding the designbasis displacement δa will be examined. Examples of estimation of the impact of δb on thebuildings and structures include investigating whether the total fracture of building mat slab
will totally occur.
In this report, secondary fault displacements were newly analyzed based on the data sortedout for past surface earthquake faults. Based on this, it has been confirmed that secondary
fault displacements are considered to be up to 30cm within the scope of this study. Thus, thisvalue can be set as δb. The annual frequency of exceedance of this value can be estimatedbased on the results of the probabilistic fault displacement hazard analysis. The
appropriateness of this value can also be verified for application.
In this report, two types of displacement are used, i.e., δa and δb. When it can be verified
that the safety functions originally required for δa can be met by δb, the analysis using δa canbe omitted.
(3) Deformation Analysis
For deformation analysis by δa, the displacement of master faults on and off the site andthat of on-site secondary faults will be estimated in a manner similar to (1) above. The
deformation of the foundation ground can be determined by evaluation based oncomputational analysis.
The impact of the displacement of the secondary fault immediately beneath the facilities isgreater than that of the deformation of foundation ground due to the displacement of thesecondary fault distantly located. For deformation analysis by δb, only the former will beconsidered.
4.2.3 Comparison of Fault Displacement with Other Event
The estimation of δa and δb in comparison with other events (natural phenomena) is shown in

8

Table 4-1.
As mentioned earlier, the location of facilities is decided based on a detailed geologicalinvestigation. Thus, the locations of the faults to analyze are clear. The regions (positions) inwhich certain impact is expected can be specified. Depending on the region, the impact on thesafety-related facilities of the plant can be mitigated by the redundancy of the systems, forexample. Therefore, fault displacements have characteristics that are different from other natural
phenomena. On the other hand, the uncertainties anticipated for them are greater than those ofother natural phenomena, including epistemic uncertainties as to whether the analysis condition(displacement) itself would occur. Thus, it is effective to analyze the impact on the facilities,
assuming δb as an amount of displacement, to assess the risk the anticipated level may have onplant safety with a view to cover mitigation measures.
Table 4-1: Positioning of Estimation of δa and δb
Status of standards
Evaluate basis event

Event exceeding evaluate

concerning thebasisestimation of event
occurrence frequency

Fault
displacement

Assessment against the design

Assessment against thebasis displacement δabeyond design basis
displacement δbCollection of JAEE
papers (Note 1)

Status of standards
Design basis event (Note 5)

Event exceeding design basis

concerning theestimation of event
occurrence frequency

Seismic
motionTsunamiAssessment against the Design
Basis Earthquake Groun
Motion Ss

Seismic risk analysis

Earthquake PRA

Seismic margin analysis

Standards (Note 2)

Assessment against the Design

Tsunami risk analysis

Basis tsunami

Tsunami resistance margin
analysis

TornadoAssessment against thereference tornado―

Tsunami PRA Standards(Note 3)
JNES outsourced
research (Note 4)(Note 1) Takao, M., et al.: Application of Probabilistic Fault Displacement Hazard
Analysis in Japan, Journal of Japan Association for Earthquake Engineering,
Volume 13, No. 1, 2013, pp17-36(Note 2) Implementation Standard Concerning the Seismic Probabilistic Safety
Assessment of Nuclear Power Plants: 2007(AESJ-SC-P006:2007)(Note 3) Implementation Standard Concerning the Tsunami Probabilistic Risk
Assessment of Nuclear Power Plants: 2011(AESJ-SC-RK004:2011)(Note 4) Research Study on the Impact of Tornadoes on Nuclear Facilities (February2011), FY2010 Outsourced Research Result Report, Japan Nuclear Energy
Safety Organization (JNES)(Note 5) Hazard analysis in the examination/analysis of the new regulatory standards by
NRA is referencing the exceedance probability of the Design Basis Earthquake
Ground Motion Ss and the Design Basis tsunami with regard to seismic motion

9and tsunami. For tornadoes, it is referencing the greater of the “maximum windvelocity in the past” and the “maximum wind velocity corresponding to theannual exceedance probability based on the hazard curve.”

10

5.

Fault Survey Method and Classification

5.1 Fault Survey Method
Figure 5-1 shows the flowchart of the on-site fault activity estimation method.
For fault activity estimation, special attention should be paid to making comprehensive
decisions based on the knowledge of “geomorphology”, “geology”, “geophysics” and so forth.
As shown in this flowchart, the “overlying strata method” is used for activity estimation. In
this method, when any strata in or before the last interglacial period are distributed, theexistence of activities since the Late Pleistocene is determined as to whether the strata havebeen displaced or deformed by any fault.

Tectonic geomorphologicalsurveyTectonic landforms, geographicalsurface classification

Grasp the possibility of activity, etc.

Boring survey, test pit survey, etc.

Strike, inclination, crush structure, breakage relations, continuity, etc.

Selecting faults for analysis

Analysis by in-fault materials

Overlaying strata method

Thin leaf observation, mineral analysis, quartz particle surface
structure, etc.

Trench surveys, etc.
breakage relations withstrataDisplacement orientation, breakage relations with altered minerals,
deformation style

Analysis criterion- Displacement of strata in and before
the Late Pleistocene
Cannot be denied

Example of analysis criteria- Style of activity in the present stressfield- Repeated activities accompanied bybrittle fractures- Activities after the formation ofaltered minerals

None

None

Fault, the activity of whichshould be considered

Cannot be denied

Fault, the activity of whichshould not be considered

Figure 5-1: On-site Fault Activity Estimation Method

11

Fault, the activity of whichshould be considered

The concept of the overlying strata method is shown in Figure 5-2. As shown in the right ofthis figure, when Stratum B covering the top of the fault is not displaced or deformed by thefault, it is determined that there have been no activities at least since the sedimentation ofStratum B. In other words, it is determined that this fault is not an active fault if Stratum B isolder than the Late Pleistocene.
Fault
断層
StratumC③層

Stratum C③層

StratumB②層

Stratum②層
B

Stratum
A
①層

Fault
断層

StratumA①層
Crush zone

Crush zone

Figure 5-2: Concept of Overlying Strata Method
When there are no overlying strata, a decision will be made in a comprehensive mannerbased on the “analysis of in-fault materials” or the geological structure development process.
Attention should be paid to the following points in examining in-fault materials:
・Whether the pattern of activity is consistent with the present stress field.
・Whether repeated activities accompanied by brittle fractures can be recognized. Whether
the fault has been formed in an environment involving plastic deformation and has been
active since then.
・Whether any activities after the formation of altered minerals can be recognized. Whether
the fault has been active after being affected by generative or hydrothermal activities indeep underground.
5.2 Fault Classification
Based on the above-mentioned detailed geological survey, faults will be classified into thefollowing four types (see Chapter 2 and Figure 2-2):・Master Faults
・Splay Faults
・Secondary Faults
・Other Faults
Generally, this sort of mechanical classification may sometimes be difficult. For example,
different opinions often arise in connection with the recognition of fault activities and their origins.
These include the decision on fault properties based on the deep underground fault distribution
profile, the decision on activity based on the state of consolidation in the fault crush zone, and theestimation of depositional ages of volcanic ashes, etc., used for the estimation of those of strata.
For any fault that cannot be denied being active, the fault in question will be considered as asecondary fault in this study. Its effect on the facilities will be estimated taking account of
displacement.
Where there are different opinions about the activity and origin of the fault in question,scientific and rational investigation should be promoted in regard to its activity and origin inparallel with the assessment against fault displacement.

12

6. Methodology of Estimation of Fault Displacement
6.1 Estimation by Field Study
When the fault’s past activity data is available from on-site geological surveys, its displacement
will be estimated based on it. Specifically, it can be estimated as displacement or deformation per
activity based on trench surveys, etc., or displacement per activity that can be computed based on
the cumulative displacement and the number of activities
6.2 Sorting out Data on Surface Earthquake Faults
Based on the surface earthquake fault data observed in Japan, secondary fault displacements
have been sorted out as shown in the figure below (see Appendix B).
Fourteen earthquakes of Mj6.5 or higher that have occurred since about 120 years before wereselected for analysis. These surface earthquake faults whose displacements are in harmony withthe activity sense of earthquake source faults were presumed to be structural faults and secondary
faults appeared near these faults were selected for sorting out their displacements. Eightearthquakes of Mj6.8 to 7.3 were accompanied by these secondary faults with displacements
ranging roughly from 0.1m to 0.3m.
In terms of the relationship between the magnitude of earthquake and secondary fault
displacements, displacements range from 0.1m to 0.2m for Mj6.8 to Mj7.0 and 0.2m to 0.3m for
Mj.7.2 to Mj.7.3, except for the Mikawa Earthquake. It is possible to estimate corresponding
secondary fault displacements by identifying the size of the master fault based on these data.

70

Displacement (cm)6050flectional area
cover stratum
bed rock

40
30
20
10
0
0

1,000

2,000

3,000

4,000

5,000

Distance (m)Figure 6-1: Distance from Master Faults and Displacement of Secondary Faults
For this study, documented fault displacements corresponding to tectonic landforms wererecognized as master faults or splay faults, while those not corresponding to tectonic landforms wererecognized as secondary faults (see Chapter 2).
Documented fault displacements are considered to have left remarkable displacements in therecords of geological surveys. Even if a detailed resurvey is performed at this point of time,
landforms have changed due to artificial modifications or natural erosion. In particular, it is highly
likely that minor fault displacements have ceased to exit. It is difficult to recognize minor faults thatare not recorded at this point of time. Considering that largest displacements have essentially beenrecorded immediately after earthquakes, it is possible to understand that this figure shows the largest
values of secondary faults although it was prepared to sort out approximately 120 years of data inJapan.
It is necessary to note that this figure includes the displacement of overlying strata as well as that13

of bedrock. According to the data on bedrock and overlying strata, however, there is no significant
difference and the displacements are roughly 30cm or less. The appearance of surface earthquake
faults is considered to vary depending on the size or location of the asperity of earthquake source
faults, crustal stress fields, physical properties, geological structures, and landforms. However, thisfigure can be referenced for the beyond design basis displacement δb in connection with fault
displacements that are expected to occur in the future.
The particularly large values in the above figure may have reflected the activity of the master
faults aligned in an echelon arrangement in a “flectional area” during the Northern Izu Earthquake or
Mikawa Earthquake. The area in which these were recorded is located at a junction of neighboringearthquake source fault segments. Since the strike of both earthquake source faults changes sharply
by 30 degrees or more, it is referred to as a “flectional area.” For fault displacement assessment, it isnecessary to note that fault displacement in a “flectional area” like this is likely to be larger,
necessitating future research and study.
6.3 Displacement Estimation by Analysis
6.3.1 Outline of Fault Displacement Analysis Methods
Here, major methods for analytically determining on-site fault displacement, including
advanced ones, are outlined. The effect of displacement will be estimated first by using theanalysis methods conventionally used in the engineering area. It is desirable to use advanced
analysis methods complementarily as many of which are still in the study phase to makecomprehensive decisions on analysis results.
(1) Dynamic Approach
As a method to estimate on-site fault displacement, dynamic model-based approach can bethought of. In this method, fault parameters, such as the fracture propagation rate, amount of
displacement, and seismic source time function, can be obtained as a result of analysis just by
giving the stress-slip relationship on the fault plane. Since the 1970s, analysis based on thisapproach has continuously been performed using the finite difference method (Reference 1),boundary integral equation method (Reference 2), and finite element method (References 3
through 7). Initially, the main objectives were to understand the occurrence and developmentof fault ruptures, and reproduce seismic motions near the ground surface. Following thedamage done by surface earthquake faults in the 1995 Hyogo-ken Nambu Earthquake and1999 Taiwan Chi-chi Earthquake, however, it draws attention as a displacement analysis
method in recent years. In the finite element method, for example, those mechanisms suitablefor fracture problems, such as the particle discretized scheme finite element method(PDS-FEM) (Reference 8), may be used in addition to those using joint elements whenmodeling faults. Figure 6-2 shows the image of the model.
In principle, it is an ideal model that allows for reproducing the movement of a fault andthat of the ground in the vicinity of the building in single model for simultaneousconsideration of dynamic effect. When the model for analysis is made to have resolution
sufficient to analyze the deformation of the ground near the building, however, a certain means
are needed because analysis is difficult with ordinary computer capacity. The further
development of this approach is desirable, e.g., investigation concerning the calibration of thestress-slip relationship on the fault plane.

14

The fault displacement occurs,
generating seismic waves.

Give a trigger, setting a stress-slip
relationship on the fault plane in theprescribed stress field.

Figure 6-2: Image of Dynamic Approach(2) Static Approach
Enforcement displacement resulting from fault dislocation will be applied statically to theboundary of the target area in which the effect on the facilities will be analyzed to computethe displacement and/or deformation of the analysis area. Enforced displacement applied tothe boundary of the analysis area is computed using the elastic theory of dislocation, etc., asshown in Figure 6-3. In the elastic theory of dislocation, other faults and buildings within theanalysis area will not be modeled. Subsequent ground deformation analysis will be described
Section 6.3.2.

Importantstructure

Apply dislocation to
the fault location

structur
Other faults

Analysis area

Output displacement distribution at
the boundary of the analysis area

Fault for whichdisplacement is
considered

Figure 6-3: Computing Displacement in the Boundary of the Analysis Area

(3) Approach by Granular Material Models
Both dynamic and static approaches are generally based on the finite element method. In
recent years, however, granular material models of the distinct element method (DEM) areused for analysis (References 9 through 12). The distinct element method can render slips andbreaks at all contact points representing granular materials, making it easy to reproduce
fracture phenomena. Figure 6-4 shows an example of analysis by the distinct element method
in static approach.

15

Secondary fault
Master fault

Figure 6-4: Example of Analysis by the Distinct Element Method (Arai, et al., 2013)

References＜Finite Difference Method＞
1) Harris, R. and Day, S.: Dynamics of fault interaction: parallel strike-slip faults, J. Geophys.
Res., Vol.98, pp.4461-4472, 1993.
＜Boundary Integral Equation Method＞
2) Fukuyama, E. and Madariaga, R.: Integral equation method for plane crack with arbitrary
shape in 3D elastic medium, Bull. Seism. Soc. Am., Vol.88, pp.1-17, 1998.
＜Finite Element Method＞
3) Tani, K.：Numerical simulation of model test of reverse fault by FEM incorporating joint
elements (in Japanese), Symposium on failure of ground and strain localization, Japan
Geotechnical Society, VIII-2, pp.215-222, 1994．
4) Nakagawa, H., et al, ：Application of nonlinear spectral stochastic finite element method tosurface earthquake fault problems (in Japanese)，JSCE journals A1, Vol.67，No.2，pp.225-241,
2011．
5) Anastasopoulos, I., Callerio, A., Bransby, M. F., Davies, M. C. R., Nahas, A. El, Faccioli, E.,
Gazetas, G., Masella, A.,Paolucci, R. Pecker, A. and Rossignol, E.:Numerical analyses offault-foundation interaction, Bull. Earthquake Eng.,2008.
6) Mizumoto, T., et al,: Fundamental study on fault rupture process and earthquake motions on
and near a fault by 3D-FEM (in Japanese), JSCE journals, No.780/I-70, pp.27-40, 2005.
7) Ariga, Y.: Study on safety evaluation method for dam against various kinds of surface
earthquake fault (in Japanese), Proceedings of the 30th JSCE Earthquake Engineering
Symposium, 3-0004, 2009.
8) Wakai, A., et al,: Efficient numerical analysis method for failure problems and its application
to earthquakes (in Japanese), Journal of applied mechanics JSCE Vol.8, (August, 2005)＜Granular Material Distinct Element Method＞
9) Taniyama, H：Development of shear bands in the subsurface layer due to strike slip fault was
examined using DEM analysis (in Japanese)，JSCE journals C，Vol.64，No.3，pp.485-494，
2008．
10) Kumar, R. P. and Meguro, K.: Applied element simulation of non-linear behavior of dip-slip
faults for studying ground surface deformation, in A Workshop on Seismic Fault‐Induced
Failures, pp.109-114, 2001.
11) Arai, N., et al,：Numerical analysis of distributed faults using DEM (in Japanese)，62th Nat.
Cong. of Theoretical & Applied Mechanics，OS10-12，2013．
＜Particle Finite Difference Method＞
12) Konagai, K. and Johansson, J.: Lagrangian particles for modeling large soil deformations,presented in 1st Workshop on Seismic Fault-Induced Failures, pp.101-108, 2001.

16

6.3.2 Ground Deformation Analysis Method
Here, the steps are described to analyze the deformation (displacement and/or deformation) andstability of the building foundation ground affected by both fault displacement and seismic motion
during an earthquake.
(1) Analyzing Ground Deformation due to On-site and Near-site Fault Displacement
The methods for analyzing ground deformation due to fault displacement and seismic motion
include advanced ones, such as the dynamic approach and granular material analysis described in
the previous section. Here, however, the method by the static approach applying conventional
methods is described.
In the current stability analysis of a reactor building foundation ground, the ground including
faults is modeled in detail and the verification seismic motion is input to verify ground stability by
the finite element method. The ground deformation analysis method described in this section is themethod that uses the ground model of this finite element method. The area accounted for by thisground model will hereafter be referred to as the analysis area.
In the heading of this section, “on-site” and “near-site” are used distinctively. In terms ofanalysis, however, there are no significant differences in the treatment of both.
This method statically applies enforced displacement to the boundary of the analysis area. To
determine the enforced displacement applied to the boundary, the aforementioned elastic theory of
dislocation and other are used.
Figure 6-5 shows the image of the ground deformation analysis method in which the amount of
displacement at the boundary is determined using the elastic theory of dislocation. This example
represents an image in which near-site fault dislocation is considered. When on-site faults are
considered, the model shown in Figure 6-6 can be used.
Other than the method using the elastic theory of dislocation, there is also a method in which
the amount of dislocation determined in Sections 6.1.1 and 6.1.2 is applied directly to the model
boundary as a vector in the fault orientation.
The items to be evaluated by the ground deformation analysis described in this section are:・ Displacement or deformation of the building foundation ground.
・ Stress distribution, strain distribution, and local safety factor distribution in the building
foundation ground.

17

Important
structure

Apply
dislocation to
the fault location

Other faults

Analysis area

Output displacement distribution at
the boundary of analysis area

Fault for whichdisplacement is
considered

Compute the boundary displacement in the analysis area with the elastic theory of dislocation.
(Other faults or buildings within the analysis area are not modeled)

Importantstructure
Other faults
Other faults

Analysis area
(Finite element model)

Statically apply the boundary displacement computed with the elastic theory of
dislocation to the finite element model in the analysis area.
Figure 6-5: Image of Ground Deformation Analysis with the Elastic Theory of Dislocation(When near-site faults are considered)18

Important
structure

Other faults
Other faults
Apply dislocation to
the fault location

Analysis area

Fault for whichdisplacement is
considered

Output displacement distribution at theboundary of the analysis area

Compute the boundary displacement in the analysis area with the elastic theory of dislocation.
(Other faults or buildings within the analysis area are not modeled)

Importantstructure
Other faults
その他の断層Other faults
その他の断層Analysis area
(Finite element model)

Fault for which displacement is considered

Statically apply the boundary displacement computed with the elastic theory of
dislocation to the finite element model in the analysis area.

Figure 6-6: Image of Ground Deformation Analysis with the Elastic Theory of Dislocation(When on-site faults are considered)19(2) Analyzing Ground Deformation due to Seismic Motion
In the current stability analysis of a reactor building foundation ground, the ground including
faults is modeled in detail and the verification seismic motion is input to verify ground stability by
the finite element method. The results are output with respect to the following items as describedin the foregoing section:
・ Displacement or deformation of the building foundation ground.
・ Stress distribution, strain distribution, and local safety factor distribution in the building
foundation ground.
(3) Steps to Analyze the Deformation and Stability of the Building Foundation GroundThe steps to analyze the deformation and stability of the building foundation ground are shownin Figure 6-7.
a. Analyzing the Deformation of the Building Foundation GroundTo take account of both fault displacement (dislocation) and seismic motion (quake) withregard to the displacement or deformation of the ground beneath the building, the grounddisplacement and/or deformation estimated in (1) and (2) above can be added up for analysis. The
same is applicable to the stress distribution, strain distribution, and local safety factor distribution
in the building foundation ground, and the foundation ground should be verified to be sound forthese analysis items.
Since there are a wide variety of analysis methods, it is desirable to use a few methods,
including advanced ones, in addition to the above. Based on these analyses, the design basis
displacement δa will be set.
Based on the probabilistic fault displacement hazard analysis, moreover, the annual frequencyof exceedance of δa will be estimated to verify that it meets the target value.
b. Analyzing the Stability of the Building Foundation Ground
Current stability analysis of a foundation ground is performed from a perspective different
from the above. Here, the sliding safety factor will be estimated from the stress caused by the
Design Basis Earthquake Ground Motion Ss, and the inclination of the building due to grounddeformation associated with an earthquake will be estimated to confirm that the foundation
ground is stable against the seismic motion and that the ground deformation resulting from theseismic motion is within the extent that would not impair the facilities.

20

- Field survey of on-site faults (Section 6.1)
- Past data on surface earthquake faults(Section 6.2)

*Including advanced
methods, such as dynamic
approach and otherapproaches that use
granular materials- Displacement estimation by analysis*(Section 6.3)

Elastic theory of dislocation

Input seismic
motionFigure 6-3

Initial stress state
analysisAnalysis of ground due to fault displacement

Sections 6.3.2 (1)(2) and (3)Figures 6-5
and 6-6

Seismic response
analysis

Section 6.3.2 (3) b

1) Displacement and deformation
2) Stress, distortion, and local safety factor
distributions
Foundation ground analysis considering fault
displacement

Maximum building
inclination associatedwith crustal
movement

Sliding safety factor

Current stability analysis offoundation ground
Analysis by finite
element method

Analysis of displacement/deformation and stability of building foundation groundSet the design basis
displacement δa(Section 4.2)

Probabilistic fault
displacement hazard
analysis (Section 6.4)
Referencing

Safety analysis of buildings and structures against fault displacement (Chapter 8)

Figure 6-7: Steps to Analyze the Displacement/Deformation and Stability of the Building
Foundation Ground21

6.4 Probabilistic Fault Displacement Hazard Analysis
6.4.1 Introduction
A methodology to estimate fault displacement at ground surface in association with an earthquake
probabilistically (Probabilistic Fault Displacement Hazard Analysis (PFDHA)) was proposed byYoungs, et al. (2003). In Japan, it has also been applied based on domestic data by Takao, et al.
(2013).
Youngs, et al. (2003) showed evaluation procedure based on diverse data on normal faults in the
U.S. Lateral faults and reverse faults have been analyzed by Petersen, et al. (2011) and Robb, et al.
(2011), respectively. Takao, et al. (2013) showed evaluation formulas based on Japanese
earthquakes associated with lateral faults and reverse faults.
Although the IAEA guideline (IAEA Safety Standard No.SSG-9) requires PFDHA for problems
posed by capable faults at existing nuclear power plant facilities (Appendix F), PFDHA has been
applied to a limited number of cases. Examples in which PFDHA has actually been applied include
the case of Diablo Canyon Power Plant (2011) (Appendix C-3).
For probabilistic analysis, two types of uncertainties can basically be taken into account, i.e.,aleatory uncertainties and epistemic uncertainties. Aleatory uncertainties can be evaluated byapplying the probability density function or the cumulative distribution function. On the other hand,
epistemic uncertainties mean those resulting from inadequate knowledge or data, e.g., when different
opinions are expressed by experts. Epistemic uncertainties are generally modeled using logic tree
branches and the weight given to them. If expert opinions vary, the logic tree method can be applied.
6.4.2 Outline of Probabilistic Fault Displacement Hazard Analysis
PFDHA is a method to estimate the frequency at which fault displacement exceeds a certain value
per year (hereafter referred to as the annual frequency of exceedance). The result is expressed in a
fault displacement hazard curve.
Youngs, et al. (2003) showed two approaches, i.e., the earthquake approach and displacement
approach. The earthquake approach referenced the probabilistic seismic hazard analysis proposed byCornell (1968). On the other hand, the displacement approach uses the characteristics of fault
displacement observed at a target analysis point. Here, the earthquake approach will be used as amore generic approach.
In the earthquake approach, the annual frequency of exceedance of fault displacement is estimatedas a sum of the frequency of displacement of two types of faults. One is the displacement of master
faults and the other is the displacement of secondary faults. Master faults are defined as the faults
closely related to earthquake source faults among other surface earthquake faults. Secondary faults
are defined as the fault displacements that occurred at the ground surface although it cannot be said
that they are closely related to earthquake source faults. Or it can be said that they are the fault
displacement that occurred secondarily or subordinately in association with the activity of an active
fault at places away from the active fault. Takao, et al. (203) did not consider the correspondence totectonic landforms shown in Section 6.2 when recognizing secondary faults.
Figure 6-8 shows the concept of estimating the annual frequency of exceedance when a master
fault runs through the analysis point (a) and when a maser fault does not run through the analysis
point (b). In the case of (a), it is necessary to estimate both the fault displacement that will occur
immediately above the F1 fault due to its activity and the fault displacement that will occur
secondarily due to the activity of the F2 fault at a place away from those faults. In the case of (b),however, the fault displacement immediately above the faults does not have to be estimated. It isgood enough just to estimate the fault displacement that will occur secondarily due to the activitiesof the F1 and F2 faults at a place away from them.

22

(a) When a master fault runs through theanalysis point(b) When a master fault does not run
through the analysis point

Analysis point
Active faults
Master faults due to active faults activities
Secondary faults due to active faults activities
In the case of (a), both the displacement of the master fault when F1 becomes active and the displacement of thesecondary fault when F2 becomes active will be estimated.
Annual frequency that the fault displacement at the analysis point exceeds d: v(d) = v(d)p1 + v(d)d2
In the case of (b), the displacement of the secondary fault when F1 and F2 become active will be estimated.
Annual frequency that the fault displacement at the analysis point exceeds d: v(d) = v(d)d1 + v(d)d2v(d)p1: Annual frequency that the displacement of the master fault running through the analysis point exceeds dv(d)d1 : Annual frequency that the displacement of the secondary faults associated with the activity of the ith active fault(Fi) exceeds dFigure 6-8: Concept of Estimation of Annual Frequency of Exceedance of Fault Displacement
by Takao, et al (2013)
The outline of the computation of the annual frequency of exceedance of fault displacement due tothe master fault as proposed by Takao, et al (2013) is shown in Figure 6-9. The computation of theannual frequency of exceedance of fault displacement due to the secondary fault is outlined in Figure6-10. The estimation formulas used in respective figures were proposed by Takao, et al. (2013).
Examples of computation by the methods proposed by Takao, et al. (2013) assuming two cases ofactive faults are shown in Appendix C-1. The examples are for two cases: one with a fault length of
20km and an average activity interval of 5000 years and the other with a fault length of 80km and an
average activity interval of 1000 years. As a reference, Figure 6-11 shows an example a hazard
curves of a secondary fault when a 20km-long active fault (moment magnitude Mw=6.5) with anaverage activity interval of 5000 years becomes active.
In this case, the annual frequency of exceedance is 10-5 or below regardless of the distance fromthe master fault. If some displacement is set deterministically, it can be decided that it would be
estimation on the safe side. From this figure, the annual frequency of exceedance of a fault
displacement of 30cm is found to be 5 x 10-6 to 10-7 depending on the distance from the master fault.
In these examples of PFDHA computation, the computational cell is set as 500m x 500m. Since
dependency on the cell size (the smaller the cell gets, the smaller the probability of occurrence of
secondary faults will be, resulting in a small annual frequency of exceedance) is known, an
appropriate computational cell needs to be set taking account of the cell size of the target facilities ina specific application.

23

P0: Activity rate of the active fault (per year)
P1p: Probability that the fault displacement due to the master fault occurs at the ground surface
when the active fault becomes active
P2p: Probability that the fault displacement occurs at the analysis point when fault displacement
due to the master fault occurs at the ground surface
P3p: Probability that the fault displacement exceeds a certain value when fault displacement due
to the master fault occurs at the analysis point
Analysis point

Ground surface

Earthquake source fault
Probability density of fault
displacement

Figure 6-9: Outline of Computation of Annual Frequency of Exceedance of Fault Displacement due
to Master Fault as Proposed by Takao, et al. (2013)

P0: Activity rate of the active fault (per year)
P1p: Probability that the fault displacement due to the master fault occurs at the ground surface
when the active fault becomes active
P2d: Probability that the fault displacement due to the secondary fault occurs at the groundsurface at the analysis point when the active fault becomes active
P3d: Probability that the fault displacement exceeds a certain value when fault displacement due
to the secondary fault occurs at the analysis point

Probability density of fault
displacement

The figure on the left by J.A. Treiman (2009)
Figure 6-10: Outline of Computation of Annual Frequency of Exceedance of Fault Displacement due
to Secondary Fault as Proposed by Takao, et al (2013)24

Annual Frequency of exceedance

30cm

LegendDistance from a master fault

Displacement m
Figure 6-11: Fault Displacement Hazard Curve (Secondary Fault) (When Mw=6.50)
References
1) Youngs, R.R., et al. : A methodology for probabilistic fault displacement hazard analysis(PFDHA), Earthquake Spectra, Vol.19, No.1, 2003, pp.191-219.
2) Takao, M., et al.:Application of probabilistic fault displacement hazard analysis in Japan,
Journal of Japan Association for Earthquake Engineering, Volume 13, No. 1, 2013, pp17-36
3) Petersen, M.D., et al. : Fault displacement hazard for strike-slip faults, Bull. Seismol. Soc.
Am. 101, 2011,pp.805-825
4) Robb, E., et al. : Probabilistic fault displacement hazard analysis for reverse faults, Bull. Seismol.
Soc. Am. 101,2011, pp.1542-1552
5) Cornell, C. A. : Engineering seismic risk analysis, Bull. Seismol. Soc. Am. 58, 1968, pp.
1583-1606
6) Jerome A.Treiman: Surface faulting and deforrmation assessment & mitigation,
http://peer.berkeley.edu/events/2009/sfdc_workshop/Treiman_PEER_JT_r.pdf

6.4.3 Issues Concerning the Expansion of Application and the Improvement of Accuracy of Hazard
Analysis(1) Issues Concerning the Expansion of Application
The uncertainty of fault displacement hazards arises from epistemic uncertainties as mentioned
earlier. It is modeled using logic tree branches and the weight given to them and expressed as thewidth of a fault displacement hazard curve (fractal hazard curve). It is considered important for the
expansion of application of PFDHA that options are provided to allow for appropriate setting oflogic tree branches and that these options cover almost all future possibilities.
To estimate the probability of occurrence, Takao, et al. (2013) used a 500m x 500m cell like
Youngs, et al. (2003). However, the probability of occurrence depends on the cell size. The resultsplotted based on the formula proposed by Petersen, et al. (2011) are shown in Figure 6.12. Making
the cell size smaller will result in a smaller probability of occurrence. It is considered as one
condition for the expansion of application of PFDHA to clarify this sort of trend with regard to
Japanese data.

25

To estimate the distribution of secondary fault distribution, Takao, et al. (203) also applied themodeling (e.g., function forms) proposed by Youngs, et al. (2003) as it is. Its appropriateness and theways to decide on parameters may need to be reconsidered.

Probability of Occurrence of Secondary Fault

Examination of Cell-Size Dependency by Petersen (2011)

Distance from Master Fault (km)Figure 6-12: Examination of Cell-Size Dependency by Petersen, et al. (2011)(2) Issues Concerning the Improvement of Accuracy
It is considered important to accumulate field survey data and utilize the results of experiments
and numerical analyses so as to complement data inadequacy and improve analysis accuracy. In casea surface earthquake fault appears in association with an earthquake, it is important to conduct fieldsurveys that will contribute to improving the accuracy of this analysis method, e.g., accuracy of theempirical formula regarding the attenuation of fault displacement.
6.5 Issues Concerning Fault Displacement Analysis
Major issues concerning fault displacement analysis include the following:(i) Nuclear power plants are sited on bedrock. The displacement information essentially requiredis the information about fault displacement in bedrock. However, it has to be said that little
information is currently available about displacement in bedrock. Displacements recorded insurface earthquake faults include those that occurred both in overlying strata and bedrock. In
general, it is difficult to discuss the quantitative relationship between fault displacements on
bedrock and those in overlying strata. Thus, it is necessary to accumulate survey data, indoor
experiments on fault displacement, and analytic evaluations. In “flectional areas” in which
different earthquake source fault segments will join with one another by sharply changing
their strikes, fault displacement is likely to be larger. It is, therefore, necessary to study andresearch fault displacements in “flectional areas.”(ii) With regard to the analysis of fault activities (ground deformation as a result), various
studies and researches are currently under way, including advanced method. It is necessary to
promote the upgrading and practical application of them. The conditions (e.g., physicalproperties and stress states) of the ground are extremely important as analysis conditions. Thus,
it is necessary to upgrade the ways to obtain the data and utilize the data obtained through26

geological and ground surveys and seismological observation in the planning, design, andconstruction of nuclear power plants.
(iii) Studies on the probabilistic fault displacement hazard analysis began recently. Itsapplication needs to be expanded while its accuracy needs to be improved. It is also necessary
to promote a series of studies, such as fragility analysis and accident sequence analysis, forplant-wide risk assessment against fault displacement hazards (fault displacement PRA).

27

7.

Load Combinations and Allowable Limits

With regard to load combinations and allowable limits, buildings and structures should have amargin in the ultimate state (deformation acceptability and ultimate strength) as the whole structure
against the effect of fault displacement in addition to the stationary load, operating load and seismic
loads. Components and piping systems should maintain the functions required for the facilities
against the loading condition combining the effect of fault displacement in addition to operating andseismic loads.
The effect of fault displacement will be evaluated based on amount of displacement at its
anticipated location, which is considered to work statically in one direction.
7.1 Load Combinations and Allowable Limits of Buildings and Structures against Fault
Displacement
The building for assessment is the reactor building containing important equipment to the safetyof a nuclear power plant. Other buildings and structures containing important equipment to thesafety than the reactor building will also be assessed.
In addition to the load arising from fault displacement, the stationary load, operating load, andseismic load will be combined. Here, the seismic load is the load arising from the earthquake
corresponding to the design basis displacement δa. The idea about the allowable limits is
described below.
・ Design basis displacement δa
Buildings and structures should have a sufficient margin of deformation acceptability(deformation at the ultimate strength) as the total system, and adequate safety margin against
the ultimate strength.
・ Beyond design basis displacement δb
Buildings and structures should maintain the shape as the whole structure without leading
to total fracture.
7.2 Load Combinations and Allowable Limits of Components and Piping Systems against Fault
Displacement
The equipment to be assessed among components and piping systems is important equipment tothe safety of a nuclear power plant. Specifically, it will be the components and piping systems(Class 1, 2 and MC) which are specified in the Codes for Nuclear Power Generation Facilities –Design and Construction Codes (Japan Society for Mechanical Engineers, JSME S NC1-2012)
from the perspective of structural design and the components and piping systems of seismic class
S (classified as highest importance), which are specified in the Nuclear Power Plant Seismic
Design Engineering Codes (Japan Electric Association, JEAC4601-2008) from the perspective ofseismic design.
With regard to load (stress) combinations and acceptable standards, acceptable standards must
be met for the load combinations specified according to the classification of components inaccordance with JSME S NC1-2012. When combining with the load from seismic motion, thecombination specified in JEAC4601-2008 will be followed.
The working loads (stress) to be specifically combined include the dead weight, pressure,external mechanical force, thermal stress, and seismic force. Along with these, the stress arisingfrom the impact of inclination, deformation, or relative displacement resulting from fault
displacement will be estimated.
The allowable stress will be based on the permissible level that has been specified for each of
the failure modes (e.g., ductile fracture, plastic collapse, buckling, fatigue fracture and progressive
deformation). The allowable stress specified for each operating mode (operating modes I throughIV) will also be applicable. The idea about the allowable limits is that the functions required ofcomponents and piping systems will be maintained for both δa and δb.
Here, it will be verified based on analysis or test results that the functions of the facilities (e.g.,28the function to maintain internal fluid) will not be affected by excessive deformation, cracking, or
damage even when a considerable portion of a static component yields, resulting in plastic
deformation. It will also be verified based on analysis or test results that the performance of a
dynamic component will not decline beyond the system’s allowable level due to plastic
deformation of moving parts. Chapter 9 outlines these.
For individual analysis using the beyond design basis displacement δb, safety analysis will be
performed taking account of the redundancy of the system or the effectiveness of consequence
mitigation measures.

29

8.

Safety Assessment of Buildings and Structures against Fault Displacement

8.1 Scope of Application“8．Safety Assessment of Buildings and Structures against Fault Displacement” will be conductedwhen assessing the effect of seismic fault displacement to buildings and structures. The displacementof buildings and structures computed in the process of the safety assessment will be used for thesafety assessment of components and piping systems against fault displacement.
The buildings and structures to be analyzed will be the reactor building containing the facilities ofseismic importance Class S. Other buildings and structures containing Class S facilities than thereactor building will also be assessed.
Examples of scope of application are shown in Figure 8.

Turbinebuilding
タービン建屋building

制御建屋

制御建屋

Control

Turbinebuilding
タービン建屋Control

Reactorbuilding
原子炉建屋

building

Reactorbuilding
原子炉建屋

On-site fault
敷地内断層

On-site
fault
敷地内断層

敷地内断層の例
On-sitefault example 1

敷地内断層の例２On-sitefault example 2
Figure 8-1: Scope of Application

8.2 Assessment Policy
For the safety assessment of buildings and structures (collectively “building(s)”), the target
building and surrounding ground will be modeled using a three-dimensional discrete system. The
seismic load and fault displacement will be applied to this analysis model to compute the resulting
displacement, stress, and so forth that will be generated in the building. The safety of the building
against displacement will be estimated based on the computation results.
In general, safety important buildings, including reactor buildings, have reinforced concrete
structures. See Appendix D-1 for the fracture properties of reinforced concrete members of mat
slabs and others when they are subjected to seismic displacement.
8.3 Material Constant
As the material constant for the building and ground, the value measured in testing will be used.
If the material constant is not measured in testing, any of the following values can be used:
・Values that are set in the design stage
・Values that are shown in the Atomic Energy Society of Japan’s “Implementation Standard
Concerning the Seismic Probabilistic Safety Assessment of Nuclear Power Plants: 2007.”

30

Estimate fault displacement
Setting design basis displacements δa

8.4 Analysis Method

YES

Mainly the mat slab
will be analyzed

No

Model focusing on
mat slab

Building-groundintegrated model

Modeling the building

Modeling the building

Shell elements or solid elements
Elasto-plasticity of the mat slab

Shell elements or solid elements
Elasto-plasticity of the mat slab

Modeling the ground

Modeling the ground
Solid elements, etc.

Computing the ground springelements
Modeling the buildingground interface

Modeling the buildingground interface
Joint elements, etc.

Building-ground system
model

Building-ground system
model

8.5 Analysis Steps

Design basis displacement δa is set
YesNo(Design basis displacement δa is a value other than 0)

Fault survey results

Design basis displacement δaGround analysis results

Building-ground systemanalysis

Safety functions concerned with themat slab

No

Yes
Deformation and inclination of the mat slab, relative
displacement between the buildings, etc.

Assessing components
and piping systems
Fault survey results

Reconsideration

Beyond design basis displacement δbGround analysis results

Building-ground systemanalysis
By incremental analysis

YES

Total fracture of the mat slab

No
Beyond design basis displacement δb
No
Deformation and inclinationof the mat slab,
relative displacement
between the buildings, etc.

Position of total
fracture of themat slab

Yes
Deformation and inclination of the mat slab,
relative displacement between the buildings, etc.

Assessing components
and piping systems

Figure 8-2: Flowchart of Safety Assessment of Buildings against Fault Displacement31

8.4 Analysis Method
8.4.1 Analysis Models(1) Types of Analysis Models
Two analysis models can be used depending on the purpose of analysis, peripheral groundconditions, and so forth.
・Model focused on mat slab
・Building-ground integrated model(2) Model focused on mat slab
When analyzing the rotating angle of the whole building against fault displacement, the “model
focused on mat slab” can be used. The “model focused on mat slab” is based on shell or solid
elements for the mat slab. The foundation ground will be modeled with the equivalent springelements. In this case, the equivalent ground spring elements will be estimated as a combined or
independent spring. An example of the analysis model is shown in Figure 8-3.
For analysis, the elasto-plasticity of the mat slab, separation and sliding between the building
and ground will be considered as necessary.
Fault displacement will be applied as boundary displacement in the horizontal and verticaldirections of the ground spring(3) Building-Ground Integrated Model
When analyzing the safety of the whole building against displacement, including the mat slab
and the rotating angle of each level of the building, the “building-ground integrated model” can beused. The “building-ground integrated model” will be modeled with shell or solid elements for themat slab and building. The ground will be modeled with solid elements, etc. Between the building
and ground, elements in which separation and sliding can be considered, such as joint elements,
will be inserted. The fault plane will be modeled with joint elements, etc. The area of the groundwill be set within a range not be affected by buildings. An example of the analysis model is shownin Figure 8-4.
Fault displacement will be applied as boundary displacement in the horizontal and verticaldirections.
For analysis, the elasto-plasticity of the mat slab, separation and sliding between the building
and ground will be considered as necessary.

Mat slab

Building
model

Equivalent groundspring element

Groundmodel
Figure 8-4: Building-Ground Integrated Model(Example)

Figure 8-3: Model Focused on Mat Slab(Example)32

8.4.2 Analysis Steps
Considering constant stress (ground stress and building’s dead weight), dead weight analysis
and seismic analysis will be performed. An example of analysis steps is shown in Figure 8-5

Step 1: Analyze effect of
the ground’s dead weight

Step 2: Analyze effect of
the building’s dead weight

Step 3: Perform seismic analysis(displacement, etc.)

Figure 8-5: Analysis Steps
8.4.3 Outputting Analysis Results
To analyze the stability of the building against displacement, the stress or strain generated ineach element and the deformation at each joint will be output.
8.5 Analysis Steps
8.5.1 Analysis against the Design basis displacement δa(1) Target of Application
When the on-site fault displacement (design basis displacement δa) has been determined as notzero based on survey results, or the results of analysis of the ground to building system with using
the ground deformation analysis model, the safety of the building against displacement will beanalyzed according to steps described below.
(2) Loading Conditions
Loading conditions below will be considered.
・Consider the condition in which fault displacement (horizontal and vertical displacement) is
applied independently.
・Consider the condition in which the seismic force of an earthquake and fault displacement
are applied simultaneously.
In this case, the seismic force will be corresponding to the earthquake that is expected tocause the design basis displacement δa.
(3) Estimating the Allowable limit
Buildings and structures should have a sufficient margin of deformation acceptability(deformation at the ultimate strength) as the total system, and adequate safety margin against theultimate strength of the buildings and structures.. Specifically, it will be verified that the stress andstrain of the mat slab and the earthquake resistant walls are within the allowable limit.
(4) Output for assessment of Components and Piping Systems
As analysis results, the deformation and inclination of the mat slab, etc., the relative
deformation between the buildings, and others will be output for the safety assessment ofcomponents and piping systems.
8.5.2 Analysis against the Beyond design basis displacement δb(1) Target of Application
With respect to the beyond design basis displacement δb, the steps described below will be used
to assess the safety of the building against displacement.

33

(2) Loading Conditions
・Consider the condition in which fault displacement (horizontal and vertical displacement) is
applied independently.
・Consider the condition in which the seismic force of an earthquake and fault displacement
are applied simultaneously.
When the beyond design basis displacement δb is set as a value that takes into accountuncertainties over the design basis displacement δa, the seismic force corresponding to theearthquake that is expected to cause the design basis displacement δa will be considered.
Here, fault displacement will be applied incrementally and the upper-bound of displacement
applied will be the beyond design basis displacement δb.
(3) Estimating the Allowable limit
Buildings and structures should maintain the shape as the whole structure without leading to a
total fracture. Specifically, it will be verified whether the mat slab and earthquake resistant wall
does not lead to total fracture (i.e., fracture across the span of the mat slab or earthquake resistantwall).

(4) Output for assessment of Components and Piping Systems
As analysis results, the deformation and inclination of the mat slab, etc., the relative
deformation between the buildings and others will be output for the safety assessment ofcomponents and piping systems against fault displacement.
When the foundation leads to total facture before the fault displacement reaches δb (beyond
design basis displacement), the fault displacement that caused the total fracture will be indicatedas the limit displacement. As analysis results of the limit displacement, the displacement andinclination of the mat slab, the displacement of each part of the buildings, etc., will be output.
Fractured zone will be specified and the relative displacement within and between the structures
will be output for the safety analysis of components and piping systems against fault
displacement.

34

8.6 Trial Analysis of Buildings and Structures against the Fault Displacement
To estimate the effect of fault displacement on the reactor building, a trial analysis was
performed. The results of trial analysis of a BWR reactor building is shown in Appendix D-2
while those of a PWR reactor building is shown in Appendix D-3.
In the trial analysis of the BWR reactor building, two cases were considered by setting therigidity of the foundation ground as Vs=500m/s (soft rock) and 1500m/s (hard rock). An
elasto-plastic analysis was performed with the building-ground integrated model in the event of a
maximum of 30cm of reverse fault displacement directly under roughly the center of the reactor
building. In the trial analysis of the PWR reactor building the rigidity of the foundation ground isassumed Vs=1600m/s in the event of 30 cm normal fault displacement on the outside of thecontainment vessel.
Figure 8-6 shows the BWR analysis model and result (deformation) while Figure 8-7 shows the
PWR analysis model and result (deformation). Here, deformation scale is enlarged 10 times.

BWR building

G.L. 0.0[m]GroundFault plane
250.0[m]G.L. −150.0[m]250.0[m]Figure 8-6: BWR Trial Analysis Model and Result (deformation, enlarged 10 times)

PWR building
Fault location

Ground spring

75m
80m

Figure 8-7: PWR Trial Analysis Model and Result (deformation, enlarged 10 times)

35

Although these trial analyses were performed for certain limited cases, it was found thatground-building integrated analysis is possible for a fault displacement of 30cm or so, making it
possible to grasp the trend of the stress and deformation occurring to the mat slab, earthquake
resistant wall, etc. of the reactor building. According to these results, the stress in the building
tends to be greater in the case of the hard ground when the same displacement is assumed. As forthe effect of fault displacement, the out-of-plane shear stress tends to be more severe than thebending moment. However, it is expected that the stress and deformation in the building will bedifferent depending on the amount, direction (normal, reverse, or strike fault), and the location of
the faulting relative to the building, ground conditions, and the type of the building (the type ofreactor, the thickness and shape of the mat slab, the arrangement of the earthquake resistant walls,
etc.)
8.7 Issues on the Safety Assessment of Buildings and Structures against Displacement
In the safety analysis of buildings and structures, the behavior of the building due to fault
displacement, etc., will be analyzed through elasto-plastic analysis taking account of theelasto-plasticity of the ground, fault plane slips, separation and sliding between the building andground, and the elasto-plasticity of the building. Based on this, the safety against displacement
will be assessed.
The method used here is a combination of conventional methods. To develop and refine themethod described here, the following issues can be pointed out:(i) Loading
Here, the displacement of the secondary fault due to an earthquake is applied statically and theseismic force arising from the earthquake is applied statically as well. However, it is desirable thatthese can be considered simultaneously and dynamically. This sort of load analysis remains to beaddressed in the future.
(ii) Stress Analysis
There are a variety of stress analysis methods and none of them are specified here. Whenperforming elasto-plastic analysis, however, it is general to use laminated shell elements for the
analysis of each part of the building due to limited computational time. Laminated shell elementsallow for detailed analysis against the bending moment and axial force. The evaluation concerning
the out-of-plane shear stress has to depend on evaluation by conventional experimental formulas.
If computational time is ignored, it is possible to apply solid elements that can express shapes ofeach part of the building exactly basis in elasto-plastic analysis. Accuracy of analysis will be
improved by applying solid elements, etc. in elasto-plastic analysis as computer capacity
improves.
(iii) Allowable Limit Evaluation
The allowable limit of the mat slab for the beyond design basis displacement δb is the total
fracture of the building. In some cases, however, it is difficult to estimate a total fracture in detailby analysis. In this case, there is no choice but to depend on conservative evaluation. The
approach to developing analysis method concerning total fractures of the building will beestablished.
(iv) Fragility Evaluation
For the safety assessment of buildings and structures, a deterministic method has been provided
to evaluate safety against the fault displacements estimated based on various studies. When fault
displacement is estimated probabilistically, however, it is necessary to establish a probabilistic
method to assess the safety against fault displacement in line with it. The method to analyze
fragility against the fault displacement will be established in the future based on the method
presented here.

36

9.

Safety Assessment of Components and Piping Systems against Fault Displacement

9.1 Scope of Application
When considering the effect on the nuclear power facilities arising from on-site fault
displacement caused, assessment is required to verify that the safety functions of “shutting down,”,“cooling” and “containing” can be maintained.
In this chapter the method is shown to analyze the effect on components and piping systems
from the inclination and deformation of buildings and structures due to on-site fault displacement
and the associated relative displacement between the buildings and structures.
The analysis described here is based on the premise that the shape of the buildings andstructures as a whole can be maintained. Cases in which the support functions of components andpiping systems are lost are outside the scope of analysis. The equipment to deal with severe
accidents, etc. is also outside the scope of individual analysis. The idea about the analysis
described in this study may be helpful in future analyses.
9.2 Analysis Policy
9.2.1 Equipment to Assess
Equipments to assess are those important to safety of nuclear power plants. Specifically, it willbe the components and piping systems (Class 1, 2 and MC) which are specified in the Codes for
Nuclear Power Generation Facilities – Design and Construction Codes (Japan Society for
Mechanical Engineers, JSME S NC1-2012) from the perspective of structural design and thecomponents and piping systems of seismic class S, which are specified in the Nuclear Power Plant
Seismic Design Engineering Codes (Japan Electric Association, JEAC4601-2008) from theperspective of seismic design. These codes are the latest at present. However, it should be notedthat older versions will be used for regulatory compliance because engineering evaluation by theregulatory body is behind the schedule.
9.2.2 Conditions for Analysis of Components and Piping Systems Affected by Fault Displacement
As the conditions for the analysis of components and piping systems, the inclination anddeformation of the buildings and structures due to fault displacement, the relative displacement
between the buildings and structures, and the seismic force*1 arising from the anticipatedearthquake will be taken into account in addition to operating loads.
With regard to the inclination, deformation, etc. of the buildings and structures for which theimpact on components and piping systems is considered, the values calculated in the process ofsafety assessment of the buildings and structures. The maximum inclination and deformation
anticipated will be the levels at which the support functions as the indirect support structures forthe target equipment can be maintained.
*1: Inertial force and force due to seismic relative displacement
9.2.3 Screening the Equipment to Analyze
Based on the levels of the anticipated maximum inclination, deformation,, etc., described in
9.2.2, the effect on components and piping systems will roughly be estimated. It is considered
possible to put the equipment for which a minor impact is anticipated outside the scope of thesafety assessment against fault displacement. Equipments on which the inclination or deformationof the buildings and structures are considered to have a minor impact are as follows.
(i) Equipment installed in the area not affected by the inclination or deformation of thebuildings and structures(ii) Equipment that will apparently receive minor impact because of the dimensions of thecomponents and piping systems and the interfaces with the indirect support structures (e.g.,reactor pressure vessel, core internals, components on floor)(iii) Equipment that will apparently receive minor impact compared to the seismic forcesconsidered in previous analyses or seismic design without consideration of fault
displacement.

37

(iv) Equipment with larger margin for the allowable limit compared to the ultimate limit of theindirect support structures (buildings, structures, etc.) (e.g., PCV liner)
Flowchart of safety assessment of components and piping systems against on-site fault
displacement is shown in Figure 9-1.
Representative equipments of BWR and PWR affected by fault displacement and the summaryof the impact evaluation are shown in Tables 9-1 and 9-2. Furthermore, a general structure andimpact evaluation method for representative equipment of BWR and PWR are compiled inAppendix E-1.
Select the equipment to analyze(Seismic class S equipment)
Results of safety assessment of thebuildings and structures

Screen the equipment toanalyze by the impact of
inclination or deformation

Inclination and deformation distribution, relative
displacement, and tolerance limit of the buildings andstructures

Layout and structural drawings of thecomponent and piping systems

Safety assessment of individual equipment*

Amount of
deformation

Amount of inclination

Relative displacement
between the buildings

Operating loads
Control rod insertingCore cooling function

Leakage resisting

Support function

Leakage resisting

Control rod
insertability

Large-sized rotating
components (emergency
DG, upright pump)Primary containment
vesselReactor foundation

Connecting piping
between the buildings
and structures

Staticcomponents

Yes

Safety impact against
displacement

Additional measures, etc.

Inertia force and relative
displacement due to an
earthquake

Dynamic
components

No

End

Figure 9-1: Flowchart of Safety Assessment of Components and Piping Systems against Fault Displacement

38

Table 9-1: Equipment Anticipated to be Affected by Fault Displacement and Summary of evaluation: BWR
Impact of fault displacement onbuildings and structures consideredin equipment analysis*1(Representative) equipment
or part anticipated to beaffected

39

Reactor, in-corecomponents/
supports
Tanks and heatexchangers/
supports
Refuelingmachine,reactor ceiling
crane/fall
prevention
devices
Reactorpedestal

Relativedisplaceme
Inclination Deformation nt between
connecting
parts

○

−

−

○

−

−

○

−

−

−

○

−

−

○

PCV liners

−

○

−

Spent fuelpool/liners

−

○

−

RCCV/piping
penetrations

−

○

○

StaticPCV pedestal
component (Mark-I, II)/
Concreteanchorage zone

Seismic loads considered in conventional seismic Seismic loads newly considered due to on-site fault
analysis
displacement *1
Impact on
equipment

Primary Secondarystress stressPrimary stress

Secondary stress

Maintenance Maintenance Componentof dynamic ofelectric
Seismic Seismic
force/
Bearing
Framefunctionsfunctionsinertia relative
deflection reactive
deformationforce
due toforce
displacement
inclination

Relative
deformation

○

−

−

−

○

−

−

−

Occurrence ofdead weightcomponent
force along
inclination

○

−

−

−

○

−

−

−

○

−

−

−

○

−

−

−

Impact ofbuilding
deformation on
supportdisplacement
and indirect
supportfunctionsLinerdeformation due
to building
deformation
Increase inreactive force
working on
pipingpenetrations
from connecting
piping

○

−

−

−

−

−

○*2

−

○

−

−

−

−

−

○*2

○

−

−

−

−

−

○

−

−

−

−

−

−

−

○

−

○

−

−

−

−

○

−

−

Connecting
piping/pipes

−

−

◎

Connecting
piping/pipe
supports andanchors

−

−

◎

−

−

○

○

−

−

−

○

−

Conduits/cables

Control rod
insertability

40

Dynamic Emergency DG
component (long horizontal
rotating
machine)Upright pump(long verticalrotating
machine)Electric
Electric countercomponent

−

○

○

−

−

−

Increase indisplacement
betweensupports
Increase inreactive force
due to piping
deformation
Occurrence oftension on
cablesIncrease infrictional force
due to channel
box deflection
during CR
insertion
Occurrence of
moment on
rotating
machine shafts
due todeformation
between support
point
Occurrence ofdead weightcomponent
force along
inclination (noimpact onelectricalfunctions)

○

○

−

−

−

−

−

◎

○

−

−

−

−

−

−

◎

−

−

−

−

−

−

−

○*2

−

−

○

−

○

−

−

−

○

−

−

−

−

○

−

−

○

−

○

−

−

○

−

−

○

−

−

○

○

−

−

−

*1: Impact of fault displacement ○: Minor, ◎: Major *2: Consideration required when structure deformation due to fault displacement has an impact on indirect support functions of components

Table 9-2: Equipment Anticipated to be Affected by Fault Displacement and Summary of evaluation: PWR
Impact of fault displacement onbuildings and structures consideredin equipment analysis*1(Representative) equipment
or part anticipated to beaffected

41

Primary coolant
equipment(reactor vessel,
in-corestructures,
steam generator,
primary coolant
pump,pressurizer)/
nozzles,
supports,
concreteanchoragezones
Tanks and heat
Static exchangers/
component supports
Spent fuel pit
crane,
polar
crane/fall
prevention
devicesRefueling water
pit, condensate
pit/liners
Spent fuel pit/
liners
PCCV/piping
penetrations

Relativedisplacement
Deformat
Inclination
betweenion
connecting
parts

○

○

−

○

−

−

○

−

−

−

○

−

−

○

−

−

○

○

Seismic load considered in conventional seismic
Seismic loads newly considered due to on-site fault
analysis
displacement *1
Impact on
equipment

Occurrence of deadweight component
force along
inclination. Decline
in pullout resistanceof frame (support
anchors)

Occurrence of deadweight component
force along
inclination
Occurrence of deadweight component
force along
inclination

Liner deformation
due to building
deformation
Increase in reactive
force working on
piping penetrations
from connecting
pipingPrimary SecondarystressstressPrimary stress
Secondary stress
Maintena
Maintenancence
of Componentof dynamic
Seismic Seismic
Bearing
electric
Relativeforce/
Frame
functionsinertiareactive
relativefunctions deflection due
deformation deformation
force
force
displacement
to inclination

○

−

−

−

○

−

○*2

−

○

−

−

−

○

−

−

−

○

−

−

−

○

−

−

−

−

−

−

−

−

−

○*2

−

−

−

−

−

−

−

○*2

−

○

−

−

−

−

−

○*2

−

42

Connecting
piping/pipes

−

−

◎

Increase indisplacement
between supports

○

○

−

−

−

−

−

◎

Connecting
piping/pipe
supports andanchors−−◎

Increase in reactive
force due to piping
deformation

○

−

−

−

−

−

−

◎

Conduits/cables

−

−

○

−

−

−

−

−

−

−

○*2

Control rod
insertability

○

−

−

−

−

○

−

○

−

−

−

−

○

−

○

−

−

−

−

○

−

−

○

−

○

−

−

○

−

−

○

−

−

○

○

−

−

−

Emergency DG
Dynamic (long horizontal
component rotatingmachine)Upright pump(long verticalrotating
machine)Electric
Electric countercomponent

−

○

○

−

−

−

Occurrence oftension on cables
Increase in frictional
force due toinclination during
CRDM insertion
Occurrence of
moment on rotatingmachine shafts due
to deformation
between support
point
Occurrence of deadweight component
force along
inclination (noimpact on electricalfunctions)*1: Impact of fault displacement ○: Minor, ◎: Major *2: Consideration required when structure deformation due to fault displacement has an impact on indirect support functions of components

9.2.4 Safety Assessment Method for Individual Equipments against Fault Displacement
The ideas about the load combinations and allowable limits applied to the safety assessment of
individual equipment are described below. The assessment method described here is based on
JSME S NC1-2012 and JEAC4601-2008 that are used in current structural design and seismic
design. It is considered to provide conservative analysis results against inclination, deformation,etc., due to on-site fault displacement.
When the safety cannot be confirmed with the conservative analysis method described here, theimprovement of the analysis methods will be considered.
(1) Load Combinations
In addition to the seismic load (the load from the earthquake) and the operating load considered
in conventional seismic design, the loads from the inclination, deformation, etc., due to on-sitefault displacement will be taken into account. In other words, the loads (i) through (iii) will beassumed to work simultaneously.
(i) Operating load *1(ii) Load from the earthquake *1(iii) Inclination and deformation of the buildings and structures, and the relative displacement
between the buildings and the structures due to on-site fault displacement*1: To be determined based on the service condition specified in JSME S NC1-2012 andJEAC4601-2008. The combination with the accident load is not required, assuming thatthe occurrence frequency of fault displacement is equivalent to that of Ss.
(2) Allowable Limit
With regard to the type of stress contributing to fracture, the impact of inclination will beconsidered as stress proportional to external force in the primary stress analysis. In the analysis of
the secondary stress arising from restraint of neighboring sections or self-restraint, the impact of
deformation and the relative displacement between the buildings and structures will be taken into
account.
The seismic load considered in conventional seismic design is the inertia force from the quake
and the seismic relative displacement. The allowable limit is set including the stress repeatedly
applied by earthquake. The deformation and relative displacement of the buildings and structurescaused by the on-site fault is the displacement working statically in one direction, which will
newly be analyzed this time. In the assessment, however, it will be treated as secondary stress likeseismic relative displacement. It can be estimated conservatively and simply by using the example
of allowable stress shown in JSME S NC1-2012 and JEAC4601-2008.
The allowable stress is specified for each fracture mode. Table 9-3 shows an example of theallowable stress for JEAC4601-2008 Class 1 piping in the service conditions Ds (when combinedwith the Design Basis Earthquake Ground Motion Ss).
Table 9-3: Example of Allowable Stress of Class 1 Piping
Stressclass
Servicecondition

Ds

Primary stress (membranePrimary stress+ bending)(torsion, bending + torsion)
When short-term
mechanical loads otherthan earthquake isincludedMin[3Sm, 2Sy ]Stress from torsion
0.73SmWhen the above is not met,stress from bending +torsion
2.4Sm

Primary +secondarystress range

Primary +secondary +peak stress

3Sm

Cumulative
fatiguecoefficient≦1.0(Sm: Design stress intensity, Sy: Design yield point)43

In general, the secondary stress arising from the impact of deformation and relative
displacement will be redistributed and weakened as a result of deformation, which will not
immediately cause fractures. Accordingly, a allowable limit can be specified to verify the safetyfunctions of individual components and piping systems depending on the extent of deformation
and relative displacement.
9.2.5

Points of Attention for Individual Analysis(1) Connecting Pipes
The important piping installed inside the building has a certain safety margin against the
inclination and deformation of the building. However, there are many connecting pipes between
the buildings and structures on the site, where on-site fault displacement has a relatively
significant impact on seismic safety.
As to the assessment standards for the piping systems anticipating displacement due to on-sitefaults, JSME S NC1-2012 and JEAC4601-2008, in which the method to estimate the impact ofrelative displacement is specified, will also be applied to consideration and evaluation of themagnitude and direction of the anticipated displacement and the way of restraint between thefacilities in the piping route.
The elasto-plastic analysis method can be applied to allow for analysis based on earthquake(seismic motion) and impact assessment of relative displacement between the buildings andstructures due to fault displacement.
The examples of trial assessment of the impact on connecting pipes from relative displacement
between buildings are shown in Appendix E-2.
(2) Support Structures
Support structures, such as containers, pipes, pumps, and valves, will receive direct impact of
the seismic load in addition to the inclination and deformation arising from fault displacement. By
applying JSME S NC1-2012 and JEAC4601-2008 for assessment, however, it is considered thatthey have a certain safety margin.
As for the anchor zones of large-sized equipment, such as the reactor containment vessel andthe reactor pedestal, it is possible to improve the accountability of seismic safety by performing
detailed assessment utilizing the information shown in (4) below and applying the elasto-plastic
analysis method.
(3) Dynamic Components
Among dynamic components, attention needs to be paid, in particular, to long rotating
equipment, such as emergency DG and upright pumps, for damage to shaft bearings and others
caused by the moment arising from floor deformation, etc. To this end, the information about thefunctional limit acceleration, etc., that have been confirmed by the verification tests conducted onlarge-sized shaking table, can be referenced.
(4) Reference Information
As for the safety assessment of components and piping systems against fault displacement,
codes and standards concerning structural design and seismic design can be applied. Here, theconcept of assessment taking account of the impact of fault displacement has been put together
based on the concepts of JSME S NC1-2012 and JEAC4601-2008.
As to the assessment of the impact of inclined buildings on components, useful examples areshown in the report on Kashiwazaki Kariwa Nuclear Power Station published after the
Niigata-ken Chuetsu-oki Earthquake by Tokyo Electric Power Co.
Other than these, there are numerous reports on the component soundness evaluation after the
Chuetsu-oki Earthquake. The policy on individual assessment in the event of exceedance of thedesign basis seismic motion and examples of application of the elasto-plastic analysis method to44

the seismic safety assessment of piping systems and components have been put together and thereport can be referred below.
・Reports on Soundness Evaluation of Rector Components after Chuetsu-oki Earthquake (April
2008, April 2009, April 2010, March 2012), Japan Nuclear Technology Institutehttp://www.gengikyo.jp/archive/soundnessreport.html (in Japanese)
According to many data of fatigue tests which were collected with the condition of pre-strain inthis report, it was conformed that approximately 10% cyclic strain indicated no notable change of
fatigue life. If this result is applied to fault displacement assessment, allowable stress condition
which is shown in section 9.2.4, seems to be remained sufficient safety margin actually against
one direction static displacement.
9.3 Assessment Summary and Issues
As the impact of ground displacement/deformation on components and piping systems via thebuilding mat slab, the safety of individual facilities against inclination, deformation, and relative
displacement between buildings and structures was assessed. Since most of the safety importantequipments of a nuclear power plant are installed inside the reactor building, fault displacement is
considered to have a minor impact on the inclination and deformation of the components andpiping systems via the ground and building.
With regard to the connecting pipes between the buildings and structures that receive a
relatively significant impact from displacement, it is possible to apply JSME S NC1-2012 andJEAC4601-2008 to estimate the impact of relative displacement and use the elasto-plastic analysis
method for detailed assessment.
As a result of detailed assessment of the impact of fault displacement on piping systems, it ispossible to absorb displacement by modifying piping routes and support structures when hardware
measures are required. As to measures for very low probability events, it is necessary to examine
the effectiveness of the measures in a comprehensive manner, including software and humanactions in terms of accident management, taking into account maintenance risks and costs, newly
arising from the hardware measures.

45

10.

Summary

The Committee has been activity for five months since its start in March this year. Since its
initial objectives have largely been achieved, this report was put together as a roundup.
Achievements and issues to be solved are summarized below.
10.1 Summary of Achievements
This study shows the framework of the safety assessment of a nuclear power plant against
on-site fault displacement. It is appropriate to assess the safety of a nuclear power plant in theevent of an earthquake, taking account of the effect of ground displacement on the plant’s safetyfunctions. In this report, the assessment procedure of plant safety against displacement issummarized, which has not been proposed previously.
(1) Policy on On-site Fault Analysis(i) An on-site fault is a fault, the outcrop of which exists on the site of a nuclear power plant,or the existence of which has been confirmed by boring survey, etc. When the movement of
this fault cannot be denied in the future, it has the potential to affect the facilities. In thisstudy, both displacement (discontinuous displacement) and deformation (continuous
deformation, such as the inclination of the ground) are considered to affect on the facilities.
The safety assessment of a nuclear power plant against on-site fault displacement will bereferred to as “the safety assessment against fault displacement.”(ii) Faults that are likely to move in the future include secondary faults and active faults(master faults and splay faults).
(iii) At a nuclear power plant, detailed information about on-site faults and active faults bothon and off the site has been obtained through in-depth geological surveys. Based on this,those faults that may move in the future will be selected. The displacement of on-site faults
will be estimated by the results of geological surveys on the selected on-site faults andanalytic evaluation concerning the displacement of on-site faults associated with theactivities of active faults on and off the site, or making engineering judgment based onthem.
(iv) To ensure the safety of nuclear power plants, design basis have been specified against
natural phenomena, such as earthquakes, tsunamis, and tornadoes. A fault displacement
equivalent to the design basis of other natural phenomena will be considered using anannual frequency of exceedance of 10-4 to 10-5 (per year) as a reference. This fault
displacement will be referred to as the design basis displacement δa. For this design basis
displacement δa, it will be verified that the safety functions of a nuclear power plant, i.e.,“shutting down”, “cooling” and “containing” can be ensured. When it is anticipated that thesafety functions may be affected, safety improvement measures should be taken.
(v) Since the uncertainty of fault displacement is considered to be greater than that of othernatural phenomena, the effect on the facilities arising from fault displacement exceeding thedesign basis displacement δa will be examined. That fault displacement will be referred toas the beyond design basis displacement δb. The analysis by δb will be performed from theperspective of risk assessment in the event of exceedance of the design basis. In this case,an analysis will be performed based on the actual strength of each piece of equipment toestimate its effect on the safety functions of the facilities. When the safety functions of the
facilities are considered to be affected, mitigation measures can also be taken.
(2) Estimating Displacements for Analysis(i) The design basis displacement δa will be estimated in a comprehensive manner by any ofthe methods listed below or by appropriately combining them.
・ Estimate the displacement of the fault that is likely to move in the future based on thegeological survey results.
・ Estimate the displacement by analysis when on-site secondary faults move by theactivities of active faults on and off the site.

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・ Estimate the appropriate displacement based on engineering judgment in reference tothe probabilistic fault displacement hazard analysis(ii) The analysis methods to estimate the effect of active faults include a variety of methods
including advanced ones. In this study, however, the conventional methods based on the
FEM analysis are described as examples. For specific application, it is desirable to use a
few methods for analysis.
(iii) The beyond design basis displacement δb will be assumed from the perspective of risk
assessment.
(iv) In this study, the displacement of secondary faults in surface earthquake faults associatedwith past earthquake is sorted out. Although it represents approximately 120 years of data inJapan, it can be referenced for the beyond design basis displacement δb.
In connection with the probabilistic fault displacement hazard analysis, moreover,examples of computation for two cases are shown (fault length of 20km with average
activity interval of 5000 years and fault length of 80km with average activity interval of1000 years).
(3) Safety Assessment of Buildings and Structures against Fault Displacement
The flowchart of safety assessment of buildings and structures in the event of
displacement/deformation of the foundation ground of the buildings and structure is shown for aseries of analysis, including analysis models, load combinations and allowable limits, andoutputting response to components and piping systems. Trial analyses were performed to assess
the effect of up to 30cm fault displacement directly under BWR and PWR reactor buildings to
grasp the trend of stress, displacement, etc., occurring to the mat slab and others.
(4) Safety Assessment of Components and Piping Systems against Fault Displacement
Concerning to the inclination and deformation of buildings and the associated relative
displacement between the buildings due to the event of displacement/deformation of thefoundation ground, the flowchart of safety assessment of components and piping systems is shownby the load combination and allowable limit etc. of the selected representative equipments to beaffected by fault displacement. Since most of the important equipment is installed inside thereactor building, fault displacement is considered to have a minor impact on the inclination anddeformation of the components and piping systems via the ground and building. With regard to theconnecting pipes between the buildings and structures that receive a relatively significant impact
from displacement, it is possible to apply the codes and standards of the Japan Society of
Mechanical Engineers and the Japan Electric Association to estimate the impact of relative
displacement and use the elasto-plastic analysis method for detailed analysis.
10.2 Issues to be addressed
Issues to be addressed concerning on-site fault survey, displacement analysis, and theassessment of affect on facilities are summarized below.
(i) As nuclear power plants are sited on bedrock, information about fault displacement inbedrock is required. However, at present little information is available about displacement of
secondary faults on bedrock. Thus, it is necessary to accumulate survey data, indoor experiments
on fault displacement, and analytic evaluations. In “flectional area” in which different earthquake
source fault segments will join with one another by sharply changing their strikes, fault
displacement is likely to be larger. It is, therefore, necessary to study and research fault
displacements in “flectional area”.
(ii) With regard to the analysis of fault activities (ground deformation as a result), various
studies and researches are currently under way, including advanced method. It is necessary to
promote the upgrading and practical application of them. In particular, the conditions (e.g.,physical properties and stress states) of the ground are extremely important as analysis conditions.
It is necessary to upgrade the ways to obtain the data47

(iii) As for the probabilistic fault displacement hazard analysis, its accuracy needs to be
improved and its application needs to be expanded. It is also necessary to promote a series ofstudies, such as fragility analysis of buildings and structures as well as components and piping
systems and accident sequence analysis, for plant-wide risk assessment against fault displacement
hazards (fault displacement PRA).
(iv) For the safety assessment of buildings and structures against fault displacement,
elasto-plastic analysis by the building-ground integrated model is used. However, how to apply thedisplacement and seismic force arising from the earthquake and evaluate the out-of-plane shear
stress remain to be established. Accuracy of analysis needs to be improved by upgrading theanalysis method. It is also necessary to establish a method to analyze the total fracture of the matslab.
(v) As a result of detailed individual analysis of the affect of fault displacement on piping
systems, it is possible to absorb displacement by modifying piping routes and support structures
when hardware measures are required. As to measures for very low probability events, it isnecessary to examine the effective of the measures, including software and human actions in termsof accident management, taking into account new maintenance risks, costs, etc. arising from the
hardware measures comprehensively.
(vi) From the perspective of defense in depth, it is important to improve the accountability ofplant risks, in comparison with the safety goals, paying attention to their impact on the probabilityof resulting in core damage or containment damage. In risk quantification, continuous efforts are
expected to reduce uncertainties in data. Furthermore, it is also expected to find a way to improve
resilience (flexible and strong organizational response capacity) while the organizations andpersonnel concerned with nuclear energy identify the risks arising from external events in an
extensive manner.
Experts from the relevant organizations need to steadily accumulate research data. Other
relevant societies, such as the Atomic Energy Society of Japan, the Japan Society of Civil
Engineers, and the Japan Association for Earthquake Engineering, need to promote cross-cutting
discussions beyond their specialty areas. For example, the Atomic Energy Society of Japan has put
together the ideas about “seismic safety” and “nuclear safety.” They are expected to promote
discussions as an extension of them. It is also desirable for the Nuclear Regulatory Agency toparticipate in discussion with the societies to incorporate new knowledge and information into theregulations.
The Japan Nuclear Safety Institute will follow up this report even after the end of thisCommittee and endeavor to solve the issues for the improvement of nuclear safety, asking theorganizations and personnel concerned for cooperation as necessary.

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ReferenceOn-site Fault Assessment Method Review Committee■Members, Presenters, and Secretariat
Chairperson
Haruo Yamazaki

Professor, Graduate School of Urban Environmental
Sciences, Tokyo Metropolitan University
Vice-president, National Institute of Advanced
Industrial Science and Technology
Research Advisor, Central Research Institute ofElectric Power Industry
Research Advisor Emeritus, Central ResearchInstitute of Electric Power Industry
Professor, Graduate School of Engineering, The
University of Tokyo
Professor, Disaster Mitigation Research Center,
Nagoya University

Vice-chairperson

Eikichi Tsukuda

MemberHiroshi Ito

MemberDaiei Inoue

MemberKoji Okamaoto

MemberMasayuki Takemura

Presenters

Makoto Takao (Tokyo Electric Power Co.); Yuji Torigoe, Tomoshi Hirakawa(Tohoku Electric Power Co.); Takeshi Kawasato, Noriaki Tomura, Toshio
Mori (Japan Atomic Power Co.); Masataka Sawada (Central ResearchInstitute of Electric Power Industry); Tadashi Annaka (Tokyo Electric PowerServices Co.); Takenobu Tanaka (Hanshin Consultants Co.); Takuma Hadano(Toshiba Corporation); Shinji Asakura (Hitachi-GE-Nuclear Energy);
Kazutada Ikami (Mitsubishi Heavy Industries); Yoshikatsu Imazuka(Obayashi Corporation); Minoru Kanechika (Kajima Corporation); Nobuaki
Miura (Shimizu Corporation)

Secretariat

Hiroyuki Ito
Yoshikazu Suzuki
Hiroaki Seki
Hirokazu Tsuji
Katsuichirou
Hijikata
Kazuta Hirata■ Date of Meeting
1st Committee Meeting
2nd Committee Meeting
3rd Committee Meeting
4th Committee Meeting
5th Committee Meeting
6th Committee MeetingTechnical Support Division, Japan Nuclear Safety
Institute (JANSI)Technical Support Division, JANSITechnical Support Division, JANSITechnical Support Division, JANSIStrategy Planning Division, JANSI (up to the end of
March 2013)
Nuclear Safety Division, JANSI

March 8, 2013
April 10, 2013
May 17, 2013
June 19, 2013
July 17, 2013
August 6, 201349

Assessment Methods for Nuclear Power Plant against Fault Displacement(Provisional Translation of Main Text)
Editor/Publisher: Japan Nuclear Safety Institute5-36-7, Shiba Minato-ku, Tokyo 108-0014, JAPAN
Tel:+81-3-5418-9312 URL:http://www.genanshin.jp/english
Ｃ JANSI, 2013 No reproduction or republication without permission○

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